Literature Review on Cognitive Impacts of In Cab Warning Systems

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  • The Canadian Railway Research Laboratory (CaRRL) was contracted by Transport Canada (TC) to review warning systems in locomotive cabs. The objectives of the study were to provide a better understanding of in cab warning system technology, characterize potential cognitive impacts, and allow for the creation of strategies to mitigate negative potential cognitive impacts. To achieve these objectives, the scope of work included the following principal components:

    1. Overviews of concurrent, multiple, or sequential warnings that arise in normal operating conditions, such as highly complex situations with multiple or sequential warnings, as well as how current locomotive crews respond to these warnings;
    2. Categorization and nomenclature of crew notifications, such as warnings, notifications, and reminders versus alarms, including recommended interaction types such as visual, audible, or haptic;
    3. Types of warnings that exist and are required in a rail operating environment, based on the type of risk assessments, such as excess speed, missed signals, the presence of work zones, and other factors;
    4. Human factors and usability implications (pros and cons) of the deployment of warning systems that act as a crew mechanism and that do not automatically enforce penalties (the train does not automatically stop if the crew ignores the warning);
    5. A summary of follow up actions for the crew after receiving a warning, such as reminders, acknowledgments, instructions on how to turn off warnings, and the potential cognitive impacts of these follow up actions;
    6. An overview of if data is captured when warnings are issued and, how that data are used for follow up or operational analysis; and
    7. An analysis of the relevant accident investigation reports identifying where warnings or the absence of warnings have failed to provide an effective barrier to unsafe conditions. This report completed the scope of work through a review of: (§2) in cab warning systems; (§3) alarm handling and train operator behaviour modelling; (§4) alarm management; (§5) human factor issues for in cab warking systems; and, (§6) alarm related accidents within the railway and other industries. The primary findings of the report are as follows. From §2, the prevention of signal passed at danger, overspeed, collisions, and train operators' vigilance are the primary focus of in cab warning systems. These systems commonly use visual and auditory alarms sequentially or concurrently to warn the train operators of a hazardous situation. Systems can be categorized into three generations: first generation, consists of a warning only system without the requirement for train operator acknowledgment or automatic brake intervention; second generation, consists of a warning system which requires the train operator to acknowledge warnings and an automated application of brakes to stop the train upon failure to acknowledge; and third generation, which enhances second generation capabilities with monitoring of train speed and an application of brakes in the event of over speed. Within the reviewed literature concerns were raised that upgrading of systems through generations has resulted in the confusing array of controls and displays, and recommend a consolidated control system and interface when possible. From §3 and §4, the ability of a train operator to handle (i.e., alarm notification, acceptance, analysis, and clearance) and cope (i.e., filtering, queuing, categorizing, similarity matching, and extrapolation) with alarms differs between persons (e.g., affected by their experience, route knowledge, and mental state) and situations (e.g., expected versus unexpected situations). Thus, both the train operator, and the context in which warning and alarms are issues need to be addressed through alarm management to ensure the intended response by the train operator. From §5, most negative cognitive impacts of in cab warning and train protection systems on train operators are a result of workload; with an under-load of the train operator resulting in boredom, fatigue, over confidence and complacency; and, an over load resulting in irrational reactions, confusion, exhaustion and low self-esteem. And, due to the potential for negative cognitive impacts, automated braking should be a result of the emergence of an unsafe situation not reliant on a failure of the train operator to acknowledge. From §6, automation related accidents in the railway industry, including the Ladbroke Grove accident in the UK, the Yong-Wen rail accident in China, and the Haft-Khan collision in Iran demonstrate that automated system failure, complacency of the train operator, inconsistency of alarm performance with user expectations, and poor alarm design and management were common reasons for most of these accidents.

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    Attribution-NonCommercial 4.0 International